192 ELEMENTARY PHYSIOLOGY. [ XVIII. 



c. The leucocytes scattered on the outside of, 

 but especially abundant within, the follicle. 



2. Examine prepared sections of a Peyer's patch 

 with the blood-vessels injected. Note the capil- 

 lary network in the follicle showing usually a 

 radial arrangement. 



3. Examine prepared sections of a Peyer's patch 

 with the lymphatic system injected. Note that 

 the injected material envelops to a greater or 

 less extent the separate follicles ; it occupies the 

 lymph-sinus spoken of above around each follicle 

 and does not penetrate into the interior of the 

 follicle. 



4. Take a small lymphatic gland (e.g. one of those 

 lying near the sub-maxillary gland in the cat or 

 dog) which has been preserved 1 in ammonium 

 bichromate 2 to 5 p. c. and cut sections passing 

 through the whole gland and including the hilus. 

 Shake the sections in a test-tube with water to 

 get rid of most of the leucocytes, stain with 

 carmine or picrocarmine and mount in glycerine. 



1 Good specimens are more certainly obtained by the following 

 method. A cat or dog is killed (best by bleeding after chloroform has 

 been given) and warm salt solution is injected into a carotid for a 

 quarter to half an hour, the lymphatic glands of the neck are then 

 cut out and placed in ammonium bichromate 5 p. c. for a few days, 

 sections are cut with a freezing microtome and shaken. In sections 

 so prepared the lymph channels are almost completely free from 

 leucocytes and by careful and more prolonged shaking they may 

 be removed very largely from the follicles and medullary cords. 



